WARNING: USE OF ANY OF THE MATERIAL IN THIS SUMMARY WITHOUT PROPER REFERENCE IS PLAGIARISM AND SUBJECT TO LEGAL ACTION.
PLEASE GIVE CREDIT WHERE IT IS DUE. A LIST OF REFERENCES IS PROVIDED AT THE END OF THIS SUMMARY. ALL MATERIAL
NOT REFERENCED IS THE WORK OF STEVE W. WOODRUFF AND SHOULD BE REFERENCED ACCORDINGLY.

SYNOPSIS

The San Fernando Valley is only 10 miles from the moderating influence of the Pacific Ocean, yet it continues to experience increasing temperature trends, lengthening summer seasons, an increase in the occurrence of 100F°+ maxima, a decline in the total number of annual freezing minima, and decreasing average diurnal ranges. These trends suggest that there may possibly be a heat island effect within the San Fernando Valley (Valley).

Six weather stations located throughout the Valley provided over 68,000 days of temperature data going back to 1927 from this year (2001) (Fig. 1.1). This data has been quality checked by the National Climatic Data Center (NCDC) in Asheville, North Carolina, and can be considered trustworthy raw material from which statistics presented in this summary have been derived.

Synoptic and mesoscale climatic influences undoubtedly affect, directly or indirectly, the Valley’s temperatures, but it seems that micro-scale influences are apparent contributors to the potential urban heat island. Buildings, paved streets, parking lots, and freeways promote a heat island effect by nature of their composition, however, it appears topography and motor vehicle emissions are most influential instigators of the Valley’s heating trend since the early half of the 20^th century.

Few anomalies exist in this alleged heating trend, and those that do arise can be attributed to short duration data sets from out-of-commission weather stations.

Ultimately, the urban heat island engulfing the Valley should raise alarming questions concerning continued construction into the foothills such as Porter Ranch, proposals for new mini-cities like Ahmanson’s Ranch, continued growth of population in response to continued housing construction, and that growth’s intrinsic relationship to the expanded use of the internal combustion engine, particularly single-passenger SUVs.

INTRODUCTION

Purpose
The purpose of this paper is to document trends in air temperature throughout the San Fernando Valley by interpreting temporal data sets formulated from the daily extreme temperature records of several Valley weather stations. It has long been suspected that the Valley has developed an urban heat island effect, however, with the exception of a scantily documented thesis by Joseph Glantz in 1977, no quantifiable information exists to either prove or disprove an urban heat island’s existence in the Valley.

There are numerous climatic influences on Valley temperatures, both at the synoptic- and mesoscales, but it is the micro-scale influences in the Valley that have had, and continue to have, a profound influence on local temperatures.

Before the Valley’s temperatures can be examined in any detail, synoptic and mesoscale climatic influences will be introduced. This information will serve as a backdrop to what occurs within the Valley. This summary does not deal with precipitation or air pollution, and only makes reference to such in context of temperature analyses. The core of this summary focuses almost entirely on quantitative analysis of temperature data.

SEASONS IN THE VALLEY

Introduction
As with all systems, the energy involved in large scales systems is intrinsically intertwined with energy of smaller scale systems. Therefore, both synoptic and mesoscale climatic phenomena will be generalized together in this chapter as a precursor to Valley temperature trends.

Synoptic scale influences on Valley temperatures include the semi-permanent North Pacific Subtropical Anticyclone (henceforth Hawaiian High) which is the subsiding northern portion of the north Pacific Hadley Cell. Other synoptic-scale climatic influences are the California Heat Low, the Great Basin Cold High, and the array of mid-latitude Pacific cyclones whose passages may be punctuated on rare occasions by tropical storms.

Mesoscale influences include the subtropical inversion misleadingly termed, “June Gloom”, diurnal land and sea breezes, and the quasi-stationary shallow cyclonic circulation off our coast known locally as the “Catalina Eddy”.

Synoptic and mesoscale climatic conditions have discernable effects on the Valley’s seasonal weather conditions. Spring and fall seasons tend to be more transitional periods than full-fledged seasons in the Valley in terms of temperature, but it is this transitional quality that makes them unique from the dominant summer and winter seasons whose temperature qualities are very discernable from all other seasons.

Spring (~March 21 – ~June 21)
As winter ends and spring begins, the passage of low-pressure troughs and their associated surface fronts become decreasingly frequent. At this time the vertical noon rays of the sun migrate equatorward from the Tropic of Cancer thus supplying north tropical and subtropical latitudes with increasing amounts of solar energy. This energy effectively reenergizes the Hawaiian High from its weakened winter state and causes it to migrate northward from 30°N latitude due to energy inbalances. Upper level Westerlies tend to follow the latitudinal ascent of the Hawaiian High (Court, 1984). Southern Californian coasts begin to experience an ever-increasing frequency of low stratus and advection fog that can be as much as 3000 ft (914.4 m) deep (Kimura, 1974). This advection fog and low-level stratus formation are collectively named “June Gloom”. June Gloom is 1 of 3 phenomena that occur in spring. The other 2 phenomena are Santa Ana Winds and Catalina Eddy conditions. The Santa Ana Winds and Catalina Eddy phenomena will be covered in more detail in the summer and fall sections of this chapter respectively.

Fall (~September 21 – ~December 21)
Astronomically, fall in the northern hemisphere begins when the vertical noon rays of the sun are at the equator and are en route to the Tropic of Capricorn. Upper-level Westerlies and the Hawaiian High follow this southerly track from 40°N latitude (Court, 1984). The southerly migration of the Hawaiian High allows for occasional atmospheric disturbances that may result in frontal passages through southern California. These fronts continue their eastward track where they end up over the Great Basin region, an area of the nation defined as being between the Rockies and Sierra-Cascade mountain ranges and encompassing southeast Oregon, southern Idaho, western Utah and all of Nevada. Pressure builds over the Great Basin becoming the source of hot, dry, Foehn-like desert winds known locally as the Santa Anas. Santa Ana wind speed is increased by the venturi effect as they squeeze through mountain passes on their way to the southern California coast averaging speeds in excess of 35 knots.

The National Weather Service Forecasting Office of Los Angeles/Oxnard (NWSFO LOX) delineates a minimum speed criterion of 25 knots in heavily populated areas, such as the Valley, in order for winds to qualify as Santa Ana Winds. Though Santa Ana wind conditions can occur into mid-spring, their “season” begins in the fall -- hence their coverage in this section.

The high-pressure cell over the Great Basin usually originates from an eastward tracking Pacific maritime high associated with the Hawaiian High. This maritime high-pressure cell stagnates over the Great Basin thus causing a surface atmospheric pressure increase resulting in Santa Ana winds. High pressure over the Great Basin may also originate from Canada, which results in more continental characteristics such as stronger pressure gradients and cooler temperatures. Some high-pressure cells may be extensions of highs over Wyoming or southern Canada, or be extensions of weakened offshore Pacific high-pressure cells (Rosenthal, 1972). Location of the high-pressure cells’ origins determines what type of Santa Ana Wind conditions will occur.

There are 4 types of Santa Ana winds in the Valley.

By far the most common is the Northeast to Southwest Type, or what I unofficially call the “Neptunian” Santa Anas. This type is purely marine in nature –hence the name– and has a westerly or northwesterly flow aloft. This type of Santa Ana occurs approximately 12 to 36 hours after a frontal passage and brings relatively warmer temperatures to the Valley.

A second type of Santa Ana is the East to West Type, so called because the preceding front is situated east to west with the high-pressure center to the north (behind) of the front. I unofficially call these “Combination” Santa Anas. These winds have a combination of marine and continental influence, hence the name. The continental influence creates a stronger pressure gradient between the Valley and Great Basin which results in stronger winds than the Northeast to Southwest Type. Santa Ana conditions of this type come 6 to 18 hours after the frontal passage and often bring warmer temperatures to the Valley.

A third type of Santa Ana is the Southeast to Northwest type (sometimes south to north) also called the “Backdoor” Santa Anas. These Santa Anas are purely continental in nature, are extremely cold, dry, and powerful in terms of wind speed. Fortunately for homeowners, “Backdoor” Santa Anas are rare. Usually a high-pressure cell is already situated over the Great Basin when this front arrives. As such these winds can come almost immediately after the frontal passage. “Backdoor” Santa Anas bring colder temperatures to the Valley. These colder temperatures coupled with wind speeds create a very pronounced windchill effect (Fig. 2.1).

A fourth type of Santa Ana condition is termed the “Wet” Santa Anas, so called because they follow the passage of a precipitous front and can supply their own windstorm precipitation events. 1 in 4 wet frontal passages precede the onslaught of “Wet” Santa Anas (Rosenthal, 1972).

Santa Anas are a lee wave phenomenon and therefore can contribute to lenticular and rotor cloud development over the Valley. These winds can also generate downslope windstorms that can create incredible downhill-advancing fires known as sundowners. Sundowners can be explained mathematically by determining the Froud number. The Froud number is the ratio of the fluid velocity to the speed of a linear shallow water gravity wave.

Fr2 = u2/gD

Super- and subcritical flow over the San Gabriel Mountains occur when the Froud number is less than or greater than 1 respectively. When this is not the case lee troughing occurs, the situation experienced with sundowners and with most Santa Ana conditions (Small, 1995). Lee troughing is covered in more detail in section 2.5 as part of a synopsis on the Catalina Eddy phenomenon.

Winter (~December 21 – ~March 21)
Astronomically, winter begins when the vertical rays of the noon sun are over the Tropic of Capricorn in the southern hemisphere. Northwesterly flow is the norm as the Pacific High weakens. The weakened Pacific High allows mid-latitude cyclones to move in over the Valley from the northwest. It should be noted that extended strato-bands from low-pressure centers passing to our north could swing up from the south as well. If these systems stagnate, then the Valley can experience winter storms lasting for several days. The clear weather after a winter storm is the result of an increase in onshore pressure gradient force (Rosenthal, 1972).

There are 3 basic types of winter storms that may pass through the Valley. They are the Northern type (high latitude), the Western type (mid-latitude), and the Southwestern type (low latitude). I unofficially term the Northern type of storms “Tracers”, the Western type “Hooligans”, and the Southwestern type are simply referred to as true “Winter” storms.

The Northern type (Tracers) originate north of 45°N latitude in the Gulf of Alaska. This type of cyclone is too far north to bring much rainfall to the Valley, and often only result trace amounts of precipitation – less than 0.005” (0.127 mm).

The Western type (Hooligans) originate between 35°N and 45°N latitudes just north of Hawaii. Their lower latitude origins allow for their centers to pass relatively closer to the Valley than their northern counterparts. Specifically, their centers generally pass over the San Francisco Bay area. This closer proximity to the Valley than Tracers translates to more precipitation for the Valley. More precipitation in Los Angeles equates to more minor traffic accidents and street flooding, hence the name Hooligans. Precipitation totals from Hooligans are generally in the realm of 1 to 2 inches (25 – 51 mm).

The Southwestern type of cyclone (Winter Storm) develops north of Hawaii yet south of 35°N latitude over the central Pacific. This type of cyclone is associated with the subtropical jet stream. Due to the warmer water’s positive effect on evaporation and closer proximity to the Valley, these storms can bring more than 2 inches of precipitation to the Valley.

It should be noted that Santa Ana Winds often punctuate these increasing occurrences of mid-latitude cyclones, particularly in late December through January.

During the winter, nocturnal land breezes become more apparent than in any other season (Kimura, 1974). Air temperatures over land surfaces drop lower at night during the winter than they do during other seasons. At the same time, air over the Pacific remains relatively warm. The result is high pressure over land relative to water and subsequent offshore air flow.

What occurs is less solar energy absorbed by land and ocean surfaces during the winter due to the increased angle of the noontime sun. As a result of this increased angle, solar rays must pass through more atmosphere before they reach Earth’s surface. The result is lower solar radiation values than experienced from more direct sun angles, therefore less energy input.

The mobile and transparent qualities of water combined with its high specific heat allow for water to moderate its temperature throughout the year. Land on the other hand is opaque, immobile and has a relatively lower specific heat than water, and these characteristics disallow land surfaces from storing as much heat energy as water. What results is a higher net loss of heat energy during the night. This net loss effectively chills the air over land far more than over water. The resulting thermal differentiation over land and water results in uneven cooling of nighttime air over these surfaces. Air over land becomes much colder and therefore denser than air over the water. The result is higher pressure over land relative to water. The pressure gradient created between atmosphere over land and atmosphere over the sea results in a net offshore flow (High-to-low flow). This land breeze brings colder nighttime temperatures to the Valley because cold air drains through from deserts since the deserts would then sit in a relatively low-pressure region. Air always flows from an area of high pressure to an area of low pressure (Energy goes from where it is to where it isn’t).

Summer (~June 21 - ~September 21)
Astronomically, summer begins as the vertical noon rays of the sun reach the Tropic of Cancer in the northern hemisphere. The Hawaiian High is at its strongest at this time and is situated around 30°N latitude (Court, 1984). The subsidence (a phenomenon associated with high-pressure systems and clear weather) occurs on the eastern side of the Hawaiian High over northern California and the Oregon coast (Kimura, 1974). Descending air heats adiabatically and continues its descent to within 2000 feet 610 m) of Earth’s surface thus creating a strong inversion layer.

Tropospheric vertical soundings taken during the 1980s from San Diego to Oakland along the California coast expose this inversion between cool, moist Marine Boundary Layer (MBL) and warm, dry air above. According to a study involving the vertical soundings, the inversion created by the subsidence of the Hawaiian High exists during 90% of the summer (Dorman and Winant, 1995). Considering the flow of the cold California Current and its chilling effect on air immediately above it, this subtropical inversion can become quite pronounced.

The normal northwesterly flow creates a mean drift slightly offshore. This offshore drift promotes coastal upwelling of cold ocean bottom water. The result is a band of cold water --as much as 9°F colder-- along southern Californian shores. These bands following the coastline of southern California can be 200-300 miles wide (from the shore out to sea). This band of cold upwelled bottom water water along the coast is the launch pad for advection fog. As relatively warm moist Pacific air masses drift over this cold-water band, heavy fog --1500 to 2000 feet thick-- develops and is carried inland by northwesterly flow (Court, 1984). Northwesterly flow is aided by the Hawaiian high and the thermally induced low-pressure system (Kimura, 1974).

The existing inversion layer vertically traps a relatively thick layer of stratus within the MBL. This stratus can also be carried onshore into the Valley via the Burbank/Glendale area. The invasion of low-level stratus and advection fog into the Valley is termed “June Gloom”.

The name “June Gloom” is misleading in that this phenomenon often occurs in July and August as well. In the Valley, the overcast layer is usually evaporated by noon local time. These layers tend to evaporate sooner in the west Valley due to its relative distance from the flat topography in Burbank/Glendale and the marine-influenced air that comes through that pass.

Having worked at the Van Nuys airport for a couple years, I have been able to get pilot reports as to the thickness of the "June Gloom" layers. On average, the uppermost stratus layer is from about 800-1,000' above ground level with tops at about 2,500' above ground level. The advection fog is at or very near ground level and can be as thick as 1000’. This translates to a stratus layer with a thickness of about 1,500' and fog layer of about 1000’ equating to layers combining to 2500’.

As the sun ascends and warms the layers they thin and expand vertically. In the years I've worked in the air traffic control tower at Van Nuys, I've noticed these layer extend to about 3,000' by around 10am before evaporating completely, leaving behind a haze with surface visibilities of 5-7 statute miles.

The subtropical inversion is lowest around San Luis Obispo slanting upward to the north and south (Court, 1984). One of the negative effects of the summer inversion layer is that it inhibits the escape (vertical mixing) of pollutants thereby creating dangerously high atmospheric pollution levels throughout the summer in the Valley. Additionally, the Valley is surrounded by mountains whose tops are high enough to metaphorically cage in pollutants and reduce atmospheric mixing thus amplifying pollution levels.

In addition to June Gloom, the Valley also experiences effects of the Catalina Eddy phenomenon during summer months.

Rosenthal (1972) states, “Subsynoptic-scale vortices or eddies frequently occur in the lee of southern California mountain ranges and downwind of the Channel Islands.” The Catalina Eddy is one such eddy. Catalina Eddy-like phenomena have also been observed in Australia, Canada, and South Africa, all of which result from the same basic conditions: Cold coastal waters and steep coastal mountains slopes. These combine to promote the conditions necessary for a Catalina Eddy event (Clark and Dembek, 1991).

Catalina Eddies are common from late spring to early fall, when occasional southerly flow and an elevated marine layer replace the normal northwesterly flow of the Hawaiian High. What occurs is a jet effect from the northwesterly winds that blows alongshore and is guided by the coastal mountains along the California bight. South of Point Arguello, a strong jet of air is sent southeastward past San Miguel and San Nicholas islands which creates the momentum that drives the eddy (Court, 1984) (Fig. 2.2).

Catalina Eddies tend to be approximately 100km in diameter (1 Rossby Radius). As pressure decreases from north to south along the California coast, lee-troughing can occur southeast of Point Conception (Mass and Albright, 1989). Considering the Froud number equation given above, lee-troughing can be understood as supercritical flow of air on the windward side of Point Conception which then transmutes to subcritical flow at the crest of Point Conception where it accelerates and hydraulically jumps on the leeward side of in order to conform to ambient atmospheric conditions downwind. This type of action would promote a surface low as a slight vacuum relative to surrounding air is created beneath the lifting airflow.

Higher inversion levels occur as the marine layer deepens during the eddy event thus rendering orographic containment of atmospheric pollutants below the crest line obsolete. Not only can air pollutants be mixed through greater vertical depths with an elevated inversion, but also the resulting increased cloudiness serves to reduce the effects of photochemical reactions partially responsible for the production of photochemical smog (Mass and Albright, 1989). Once the pollutants have been mixed to higher elevations, they are carried northward out of the Valley. According to Wakimoto (1987), tropospheric ozone levels also drop during an eddy event.

Catalina Eddies bring more moderate temperature conditions to the Valley and the greater Los Angeles area with warmer daily minimum temperatures, and cooler daily maximum temperatures due to the latent heat of condensation and vaporization respectively (smaller diurnal ranges). Cleaner air and moderated temperatures prove the Catalina Eddy to be a welcome respite from an otherwise hot, dry and polluted summer season.

The sea breeze is more pronounced in the summer than in any other season as well. The positioning of the Hawaiian High over the north Pacific and the thermal low over southwestern Arizona creates a pressure gradient that promotes this sea breeze (Kimura, 1974). The Santa Monica Mountains block much of this marine influence from reaching the Valley directly. However, some marine-influenced air sometimes reaches Burbank/Glendale where topographic isolation from the ocean is miniscule.

Valley Temperature Trends and the Urban Heat Island Effect
Average temperatures in the Valley appear to be gradually increasing through time. All temperature stations in the Valley show a heating trend, and most show this trend in all 4 seasons. I hypothesize that this heating trend may be the result of an increase in greenhouse gases within the Valley, as well as continued and expanding urban coverage over natural landscape where synthetic surfaces absorb and re-emit long-wave heat radiation at higher rates than natural surfaces. Some of the most dramatic increases have occurred since urbanization began to take shape on the Valley floor in the 1950s.
It should be stressed here that these heating trends are not expected to continue indefinitely and will certainly reach an apex. However, even small increases will have profound effects on many natural niches.

In the case of a valley (indeed, a city) where few travel without a motor vehicle --where distances are measured with time increments rather than distance measurements (e.g. "It's a five minute drive" as opposed to "It's about 3 miles from here")… where more people likely means more motor vehicles… where the daily use of these vehicles results in millions of tons of greenhouse gas emissions not generated otherwise – Greenhouse gas production may very well be at a high enough rate to affect long-term temperature trends.

The mountains that surround the Valley may be containing these gases effectively enough to allow them to absorb and reemit heat energy at rates higher than that of a normal mixture of atmosphere. The inversion created by the Hawaiian High is known to exist 90% of the time during the summer and about 50% of the time during winter as explained earlier (Dorman and Winant, 1995). This inversion exists approximately 2000’asl. At this height, this inversion could effectively contain pollution within the Valley whose surrounding mountains elevations are above 2000’asl.

Such conditions can create cities that are generally warmer than the surrounding, more rural areas. This relative warmth to the surrounding areas is referred to as an urban heat island (Fig. 3.1). The reason the effected city is warmer than its hinterland is due to a difference between energy gains and losses of each region. Solar energy is absorbed by surfaces both in the Valley and in surrounding less-developed regions, however, since the Valley is more urbanized in terms of non-permeable/non-porous physical structure, it is unable to retain as much water as surrounding natural areas. This makes evaporative cooling processes less effective in the Valley.

Also, the thermal properties of buildings, tar, asphalt, brick and concrete add heat to air by conduction. These materials are better conductors than most vegetation and can release heat throughout the day and night. The most dramatic contributor to the urban heat island effect is waste heat and greenhouse gas emissions from buildings, cars, trucks, trains, and aircraft. Heat contribution from these sources can be as much as 1/3 of that received by solar energy (Lutgins, 1998).

Data Analysis of Extreme Daily Temperatures
Temperature calculations of daily maxima taken from the Sunland, Burbank, and the Pierce College weather stations show increasing annual occurrences of 100°F+ days. This increasing trend of extreme maximum temperatures is indicative of an existing urban heat island within the Valley (Fig. 3.2-3.4).

Extreme minima have also been affected by the heat island. Calculations taken from the San Fernando, Sunland, and Pierce College weather stations show the total number of annual freezing minima are in decline. Pierce College is of particular interest because this station has traditionally exhibited the most extreme temperatures in the Valle. As such, it would seem that Pierce College would be most resistant to a declining trend in annual freezing temperatures (Figs. 3.5-3.7).

Approximate periods of when freezing temperatures occur were figured for 4 Valley stations; Pierce College, Burbank, Sunland, and San Fernando. Based on 180 years of minimum temperature data taken from 4 aforementioned weather stations, the first freezing minimum temperatures generally do not arrive until late December. It should be noted that Pierce College begins receiving freezing temperatures about a month earlier than the rest of the Valley; usually in late November.

Freezing temperatures continue to occur on occasion in the Valley until around early March, thus making the “freezing season” a 2 1/2 month affair from late December to early March each year. San Fernando freezing temperatures tend to linger into late March possibly due to a nighttime country breeze from the north generated from heat island convection. This will be discussed later (Figs. 3.8-3.11).

Alleged Spring Heating Trend
This summary defines spring as encompassing the months of April, May, and June. Based on 112 years of temperature data compiled from Burbank and Pierce College weather stations, mean spring temperatures in the Valley are increasing at a rate of approximately 1°F every 19yrs. San Fernando data was not used to determine this rate because the data at this station terminates in 1974; a time before some of the most dramatic increases in temperature began to occur. Nevertheless, San Fernando was also experiencing a heating trend up to the point of its termination. A mean springtime heating trend is also apparent in North Hollywood, but was not figured into the overall rate because of that station’s relatively small data set and early termination in the 1960s (Figs. 3.12-3.15).

Using the same data sets as above, spring maximum temperatures are increasing at a rate of about 1°F every 14 years, while spring minimum temperatures are increasing at a rate of about 1°F every 23.5 years. With the exception of spring maxima at San Fernando, both Burbank and Pierce College continue to show increasing temperature trends (Figs. 3.16-3.22). NOTE: All anomalies appearing not to support the heat island theory in the Valley, such as the cooling trend of seasonal maxima in San Fernando, will be collectively dealt with later in this summary.

Alleged Summer Heating Trend
Using Burbank and Pierce College temperature data, calculations show that mean summer temperatures are increasing at the rate of 1°F every 26yrs. The San Fernando and North Hollywood weather stations also show increasing mean summer temperatures, however, their data was not figured into the overall rate because of their early terminations in the 1970s and 1960s respectively (Figs. 3.12-3.15).

Using the same data sets as above, calculations show that maximum summer temperatures are increasing at a rate of 1°F every 26yrs, while minimum summer temperatures are increasing at a rate of 1°F every 26yrs. Data from the North Hollywood station showed increasing extreme temperature trends as well, however the data from this station was not figured into the overall extreme rates due to the station’s early termination (Figs. 3.16-3.22).

Alleged Fall Heating Trend
Using Burbank and Pierce College temperature data, calculations show that mean fall temperatures are increasing at the rate of 1°F every 46yrs. Mean fall temperatures were also on the rise in North Hollywood before that station’s termination in the 1960s (Figs. 3.12-3.15).

Using the same data sets from Burbank and Pierce College, calculations show that maximum fall temperatures are increasing at a rate of 1°F every 36yrs, while minimum fall temperatures are increasing at a rate of 1°F every 55yrs. Fall minimum temperatures were increasing at the San Fernando and North Hollywood stations before their terminations. NOTE: North Hollywood also was showing an increasing trend in maximum temperatures (Figs. 3.16-3.22).

Alleged Winter Heating Trend
Again, using Burbank and Pierce College temperature data, mean winter temperatures are increasing at the rate of 1°F every 55.5yrs. Mean fall temperatures were on the rise in North Hollywood before its termination in the 1960s (Figs. 3.12-3.15).

Using the same data sets, calculations show that maximum winter temperatures are increasing at the rate of 1°F every 51yrs, while minimum winter temperatures are increasing at the rate of 1°F every 60yrs. North Hollywood and San Fernando both showed increasing minimum temperatures before their terminations. North Hollywood showed increasing maximum temperatures as well (Figs. 3.16-3.22).

The varying rates of seasonal temperature increases will be discussed later.

Non-Astronomical Definitions of Seasons for the Purpose of Exposing Local Temperature Trends
It is a well-established fact that seasons are defined astronomically. The Tropic of Cancer, the Tropic of Capricorn, and the Equator all represent points that are reached or crossed by the vertical noontime rays of the sun at the beginning of a particular season. However, for purposes of exposing temperature trends in the Valley, I have unofficially redefined seasons quantifiably using temperature criteria.

By defining seasons by temperature values relative to historical Valley temperatures, I am able to show interesting trends concerning seasonal durations. I am also able to show approximate dates of when seasons begin in the Valley.

Thermally Delineated Seasons – Defining Seasons Locally
Seasons are defined here by using 2 major temperature criteria as well as specific degree-day thresholds.

The first criterion is a maximum temperature threshold for a particular season. For summers, this maximum is unlimited as long as it is above 80°F. For spring and fall seasons it is 79°F. For winters it is 69°F.

The second criteria is a minimum temperature threshold for a particular season. For summers this minimum is 80°F, for spring and fall seasons it is 70°F, and for winters it is unlimited as long as it is below 69°F.

Though spring and fall both fall into the same range of temperatures, the direction of the temperature change trend over time will delineate whether the range represents spring or fall. Specifically, fall temperatures tend to decrease as they approach the winter, and spring temperatures tend to increase as they approach the summer. Therefore, spring begins when the minimum end of the range is reached and fall begins when the maximum end of the range is reached. Continuing this logic, spring ends when the maximum end of the range is reached and fall ends when the minimum end of the range is reached. Summer and winter are simply anything at or above 80°F or at or below 69°F respectively.

The idea that springs tend to be warmer than falls comes from temperature analysis taken from dates that fall within astronomically defined seasons. However, by quantifying both the fall and spring seasons by the same temperature-defined parameters, one should not assume both seasons will have the same mean temperature. It is very likely that fall seasons will have more daily temperatures in the lower portion of its range whereas spring seasons will have more daily temperatures in the higher portion of its range. This would result in warmer springs and relatively cooler falls even though both are relegated to the same temperature range. Also --as will be seen in subsequent paragraphs-- temperatures outside the defining range can occur within a particular season. For instance, we will see why it is possible for spring to have 80°F or warmer days and fall to have 69°F or cooler days and still be considered spring and fall respectively, even though their temperature range criterion doesn’t cover temperatures above or below 80°F and 69°F respectively.

Temperatures chosen to define the limits of each season were derived from 173-year averages taken from astronomically-defined seasons from 5 Valley stations: Burbank, San Fernando, North Hollywood, Sunland, and Pierce College. The temperatures picked were chosen because they occurred around the time of the solstices or equinox (depending on the season being defined). For instance, 69°F was chosen as the beginning of winter because this was the temperature most common around the time of the northern hemisphere’s winter solstice. It should be stressed, however, that the first occurrence of a seasonal temperature threshold does not mark the beginning or end of a particular season. The determining temperature must be first in a 5-day sequence of that threshold temperature. Temperatures higher or lower than the threshold are considered depending on the season being determined.

Consider the beginning of summer for example… so far I have defined the beginning of summer as being the point in the year when an 80°F temperature is reached. However, there might be an 80°F day followed by a 79°F day. If this is the case, then that 80°F day does not represent the beginning of summer. The beginning of summer begins on the first 80°F day or warmer that is followed by 4 more days with 80°F or warmer temperatures (a 5-day sequence of ≥80°F). The same holds true for both minimum values and degree day values (Fig. 3.23). The latter two criteria will be described in subsequent paragraphs.

All 4 seasons can be put into 1 of 2 groups. Relatively speaking, there is a warm group and a cool group. In the Valley (northern hemisphere) it makes sense to place fall and winter in the cool group and spring and summer in the warm group based on local historical temperature trends. By classifying seasons in this manner one is able to distinguish the 4 seasons from each other with 2 separate linear depictions (a “cool” line and a “warm” line). Simply as an illustration, not as a graph, one can see the symmetry of these quantified seasonal thresholds (Fig. 3.24).

In addition to week-long maxima and symmetrically quantified seasonal thresholds, I have also delineated the beginnings and ends of seasons with minimum temperature values as well as degree-day values. Again, simply as an illustration (not as a graph), these thresholds can be illustrated as having symmetry. Their defining degrees must be repeated for 5 straight days in order to be considered the beginning or end of a season
--like the maximum temperature criterion-- and based on that 5-day requirement, seasons are allowed to contain minimum temperatures and/or degree days that are outside that particular seasonal range so long as they don’t continue for 5 or more days in sequence. As with maximum temperatures, this allows for fall to be cooler than spring and vice versa since lower or higher temperatures than the defining criteria can be considered when determining seasonal temperatures.

The minimum temperatures and degree-day values chosen to define the limits of each season were derived from the same 173-year averages taken from astronomically defined seasons from the same 5 Valley stations as were used for maximum criteria. For summer, the minimum range is 55°F or warmer, and the winter minimum range is 44°F or cooler. Fall and spring share the same temperature range of 45°F to 54°F, the only difference being that fall tends to be introduced by the warmer end of the range and spring tends to begin with daily temperatures on the cooler end of the given range. If illustrated as the maximum temperatures have been --in a linear depiction-- the minimum criteria will show symmetry.

Two types of degree-days are heating-degree and cooling-degree days. Degree-days are determined by the number of degrees Fahrenheit the daily mean temperature is from 65°F. For every degree Fahrenheit above 65°F a cooling-degree day is counted. For every degree Fahrenheit below 65°F a heating-degree day is counted. For instance, if the day’s mean temperature is 71°F, then the day’s degree day count is 6 cooling-degree days. If the day’s mean temperature is 60°F, then the day’s degree day count is 5 heating-degree days. Days whose mean temperature is 65°F, have no degree days.

The range of degree days used to determine the beginning of spring was 5 heating-degree days to zero degree days. For fall it was zero degree days to 5 heating-degree days, which is the same range as spring however, fall tends to begin with few or no heating degree days and spring tends to begin with more heating degree days. The summer degree day range used was 1 cooling-degree day or more, and winter was 6 heating-degree days or more (Fig. 3.23).

With 3 symmetrically illustratable delimiters for each season’s beginning and end, I am now able to better pinpoint the date where a season starts. Using a table program, I define 4 columns from left to right as Date, Maximum, Minimum, Degree Days respectively. Dates run in chronological order from top to bottom, and maximum, minimum, and degree day occurrences correspond to their respective dates. This was done for all available data from the 5 aforementioned weather stations. Once this was done, calendar years were separated out and each of the latter 3 columns for each year were analyzed to find defining criteria (henceforth, defining occurrence) according to the parameters described on previous pages. NOTE: Rarely did all 3 (or even 2) criteria occur on the same date.

The appropriate temperature or degree day was circled that fulfilled the seasons’ requirements. The first defining occurrence, whether it be the maximum, minimum, or degree day, was given the number “1”. The second was given a number based on how many calendar days away from the first defining occurrence it was. If it occurred on the 7th of a particular month and the first occurrence was on the 2nd of that same month, then the second occurrence would be given the number 6 because it is the 6th day from the first defining occurrence. The same holds for the third and final defining occurrence.

Considering the given example, if the third occurrence happens on the 24th, then it would be given the number 23 because it is the 23rd day from the first defining occurrence. The sum total of these three given numbers is divided by three to arrive at an average value. In this case the average would be the number 10. With this average, I added 10 days from the first day of the first occurrence, and the day I arrived at would be defined as the first day of whatever season I was defining. In the given example, the date I would have arrived at would be the 11th of that month (Fig. 3.23).

Results of Thermally-defined Season Analyses
Based on 173 years of data from 5 Valley stations, using the techniques outlined above, summer is the dominating season in the Valley averaging 135 days in length (Fig. 3.26). Fall and spring are by far the shortest seasons averaging only 46 and 78 days respectively. On average, Valley winters last the remaining 105 days. The Valley is dominated by the extreme seasons (summer and winter), but particularly summer with almost no fall to speak of (which may explain the lack of fall colors on Valley trees during the months of September to December).

Using the same data, the beginning and ending dates of each season within the Valley can be pinpointed. Spring arrives March 2 and occupies 29% of the calendar year. Summer arrives on May 19 and occupies 37% of the calendar year. Fall arrives on October 1 and only occupies 13% of the calendar year. Finally, winter arrives on November 16 and occupies 21% of the calendar year (Fig. 3.27). Because these dates have been arrived at based on variable temperatures, they will change over the years slightly and ought to be updated every 30 years in the same manner as “normals” are. This method of determining seasons proves useful for local studies, particularly in topographically isolated areas such as valleys.

Normal temperature and precipitation values are arrived at by figuring 30-year averages. Normals are adjusted every 10 years. To explain, normals currently used for temperature and precipitation values are derived from averaged 1971 to 2000 figures. In the 1990s normals were derived from 1961-1990 figures, in the 1980s they were derived from 1951-1980 figures and so on. Considering the techniques used to arrive at defining seasonal dates, one can figure out normal dates when seasons begin, and then adjust these dates accordingly every 10 years using the same 30-year standard in use for determining normal temperatures and precipitation averages. Seasons can be determined as arriving late or early by using normal statistics based on non-astronomical temperature criteria as outlined earlier. Temperature thresholds will differ depending on the purpose and locality of the research, but as long as they occur close to the time of the astronomical season and can be illustrated as having symmetry, they should prove useful for the researcher.

Next, I looked at seasonal durations using decadal-dependent data sets. The results show stations throughout the Valley are experiencing gradual increases in summer durations through each decade (Figs. 3.28-3.29). This increase in summer duration is encroaching on the already short, fall season. This encroachment, obviously, results in decreasing fall durations (Figs. 3.30-3.31). The lengthening of summer seasons is a trend that is indicative of a growing urban heat island in the Valley.

Greenhouse Gas Emissions and Valley Temperatures
Urban growth on the Valley floor not only changes the natural landscape to a coverage that is more heat conductive, but it also changes the chemical makeup of the atmosphere above it as more and more vehicles are introduced. Greenhouse gas emission into the air above the Valley floor appears to be a defining cause to the Valley’s heating trend.

Greenhouse gases are gases whose molecules are of sizes that allow them to absorb infrared (IR) radiation in the 5-17 micron wavelength range. Solar energy is absorbed as relatively short wave radiation is converted and re-emitted as a longer IR wavelength thus warming the atmosphere on its journey to space. Earth naturally produces greenhouse gases which serve to absorb some of the re-emitted terrestrial IR radiation. These gases absorb then convert this radiation and re-emit it back down again towards Earth thus warming the lower troposphere to bio-friendly temperatures. Some of the main greenhouse gases that occur in nature include carbon dioxide (CO2), oxides of nitrogen (NOx), Methane (CH4), and water vapor. Extremely powerful greenhouse gases that are purely synthetic in nature include hydrofluorocarbons (HFCs), perfuorocarbons (PFCs), and sulfur hexafluoride (SF6) which are results of various industrial processes.

According to the Environmental Protection Agency (EPA), some important facts pertaining to the heat capacity of these gases include:

Methane [absorbs] over 21 times more heat per molecule than
carbon dioxide, and nitrous oxide absorbs 270 times more heat
per molecule than carbon dioxide. HFCs and PFCs are the most
heat-absorbent [of all the greenhouse gases] (EPA, 2001).

Unfortunately, blind technological optimism has spurred the production and subsequent use of motors, manufacturing and agricultural methods that produce excess greenhouse gases as a byproduct of their function(s). In addition to this, greenhouse gas emissions can come from dumps and oilrigs still in use or not. A large portion of the east and northeast Valley (around the 5 and 170 freeways) used to be used as waste disposal sites decades ago. Even though these sites are no longer being used, they still emit methane gas as the organic wastes underground continue to decompose. There are still dumps in operation in the Valley, including Sunshine Canyon. I unsuccessfully applied for a job at this dump to monitor methane gas emissions a few years ago, the point being that Sunshine Canyon is keenly aware of such emissions, though it should be noted that such emissions are expected at dumps (and graveyards).

There are still many carbon dioxide emitting oilrigs scattered around the Valley, as well as flaring practices being used at a natural gas acquisition facility in the Santa Susana Mountains. Natural gas flaring is a practiced used to burn off gas in order to relieve rising pressure or to dispose of small quantities of gas that are not commercially marketable. This flaring practice results in the production of carbon dioxide.

The Valley is home to 3 airports: Burbank, Van Nuys, and Whiteman. It should be noted that the Van Nuys Airport the busiest airports in the nation for general aviation, and in fact held the distinction of being the busiest general aviation airport in the world. Data obtained from the Van Nuys airport show that total sorties in and out of that airport had jumped from 110,214 in 1950 to 618,694 in 1976 (Fig. 4.1). Just under 600,000 sorties were flown in and out of the Van Nuys airport in 1999 alone (LAWA, 2000). Whiteman is a much smaller operation, but can easily support over 100,000 sorties a year. Burbank almost parallels Van Nuys in total number of annual operations, and has a higher percentage of larger aircraft sorties. Though information on how much NOx and CO2 is emitted from large commercial and commuter sized aircraft is not available to the public (gee I wonder why?), it would seem logical to conclude that aircraft emit higher levels of these gases than any car or truck.

According to the EPA, average annual emissions and fuel consumption for passenger cars and light trucks is based on 12,500 annual miles for cars that get 21.5mpg and 14,000 annual miles for light trucks that get 17.2mpg. Based on these modest standards, the EPA determines that cars emit 1.39 grams per mile of NOx and 0.916 pounds per mile of CO2. Light trucks emit less NOx but more CO2, exuding 0.81g/m and 1.15lbs/m of each respectively (EPA, 2001). I was unable to obtain information on gallons of water vapor emitted per mile, but this greenhouse gas should be remembered as a greenhouse emission from vehicles nevertheless. Standing in site of the 118 freeway at 11am on a weekday, I counted 97 vehicles pass in front of me in a 1 minute period. If this number is doubled to count the vehicles which would have passed me on the other side, I would have a total of 194. Granted, the 118 isn’t the busiest freeway in the Valley, nor is 11am on a weekday the busiest hour, but alarming totals for Valley freeway traffic can be guessed at with some insight. (NOTE: The 405/101 junction in the Valley is the most congested freeway in the world. Idling vehicles make for inefficient energy consumption… = pollution.) Multiplying 194 by the total number of minutes in a day equals approximately 280,000 vehicles a day. There are 6 distinct freeways in the Valley, and when calculated with the above product the total is 1.68 million vehicles on freeways in the Valley per day. Considering there is approximately 1.5 million people living in the Valley (I exclude Glendale), and I conservatively assume that 30% of them are out driving on Valley surface streets at any given time, that gives me a total of 450,000 vehicles on the streets. Adding 450,000 street vehicles and 1.68 million freeway vehicles, each emitting an average of 1.1g/m of NOx and 1.2lbs/m of CO2 (averaged from car and light truck figures from the EPA), and that each of these 2.13 million vehicles averages 35 miles a day, the Valley ends up with a daily NOx and CO2 input of 82 Megagrams and 89.5 million pounds of NOx and CO2 respectively. I don’t really want to emphasize the idiocy of the EPA using both metric and English methods of measurement for two different gases of the same state, but I do want to reemphasize the fact that NOx absorbs 270 times more heat energy than CO2.

Combining the emissions produced by old and existing dumps, oil and gas rigs, aircraft from 3 airports, trains, and millions of cars, light trucks, big rigs, and buses, it is no surprise that temperatures in the Valley have raised so much since the turn of the century.

Diurnal Ranges: Illustrating the Transitional Microclimate and Greenhouse Gases
Local topography combined with the inversion described earlier affect Valley temperatures in that they act as a barriers to external low-level influences thus trapping greenhouse gases emitted at low elevations. The surrounding mountains also serve to separate the Valley from the deserts and ocean.

First we will look at how diurnal ranges show the Valley to be in a transition zone, and then we will look at how these same diurnal ranges show there is an increasing presence of greenhouse gases in the atmosphere above the Valley floor. The diurnal range is the temperature difference between the two extreme temperatures (maxima and minima).

More extreme temperatures occur in the mountains and deserts to the north of the Santa Susana Mountains and to the northeast of the San Gabriel Mountains. More moderate temperatures occur along the coasts south and west of the Santa Monica and Simi Hills respectively. Geographically, the Valley is located in a transition zone between marine and continental temperature regimes (Glantz, 1977).

Being in a transition zone, the Valley exhibits both marine and continental temperature extreme characteristics. Burbank, in the east Valley, exhibits the most marine-like extremes because of its proximity to the “Narrows” (an area of flat topography exposed to marine air).

Basically, the “Narrows” is a gap in the topographical barrier that separates the climatically marine coasts from the more continental-like Valley (Csa climate). As such, Burbank experiences smaller diurnal ranges than other parts of the Valley. The western and northern ends of the Valley are much more continental in nature. These sections of the Valley experience larger diurnal ranges than in the southeastern portion of the Valley because of their distance from any topographical gaps to the ocean.

The best examples of areas in the Valley that quantifiably illustrate the marine and continental dichotomy are Pierce College and Burbank (at opposite ends of the Valley). Based on 50 years of daily temperature data collected from 1950 to 1999, continentally influenced Pierce College averages a 7°F greater diurnal range than the marine-influenced Burbank station.

Topography not only acts to separate the Valley from purely continental and marine climates, but it also serves to contain greenhouse gases. The containment is most efficient during the summer months when the inversion from the Hawaiian High is strongest (at the 2000-foot level). To see if there is a general increase of greenhouse gases in the Valley, I looked at the trend of diurnal ranges over time. If there is increasing levels of greenhouse gases in the air, I would expect to see two things. One would be an overall increase in temperatures throughout the Valley. The second would be a gradual decrease in the diurnal range between extreme monthly temperatures. The first has been established as an apparent occurrence in the Valley based on data presented earlier, the latter is demonstrated in figures 4.2 and 4.3.

What these two graphs show (Figs. 4.2 & 4.3) is a general decline in diurnal ranges thus suggesting that latent heat from greenhouse gases is moderating one of the temperature extremes. Based on quantified evidence of increasing 100°F+ maxima, decreasing freezing minima, and looking at all the temperature charts showing heating trends, we can see that the extreme temperatures being moderated are the minima. What is likely occurring is a nighttime heat flux from lingering greenhouse gases (as well as terrestrial radiation from urban structures), which are keeping minimum temperatures warmer than they otherwise would become. The result is a warmer low and a smaller diurnal range between the extremes.

What is perhaps more interesting, is the fact that diurnal ranges do not decrease in winter and spring months, a time when the inversion from the Hawaiian High is at its weakest or even non-existent (Figs. 4.4-4.5). This supports the idea that the topography of the mountains encompassing the Valley and the inversion from the Hawaiian High act together to contain greenhouse gases above the Valley floor. Possibly, this is why diurnal range temperatures decrease in summer and into fall months, then lose this trend and increase in the winter months (as outside influences invade the Valley’s atmosphere) and continue into the spring before the inversion can reestablish itself. <<run-on sentence… I know.

Some other interesting possibilities as to why diurnal range temperatures decrease during months with a strong inversion present include swimming pools and vegetation (though slight). Figure 4.6 is a photograph I took from a Cessna over West Hills on the northwest end of the Valley near the Chatsworth Reservoir. Notice the number of pools in relation to the number of houses.

The street bisecting the neighborhood from the massive parking lot is Fallbrook Ave. In addition to showing the density of pools and imported vegetation in the neighborhood, this photograph also shows the other extreme of human interference on the natural landscape of the Valley… a parking lot. Massive parking lots such as the one shown in this photograph have enormous heat capacities.

During the warmer summer months and into fall, evaporation rates are considerably higher than they are in any other time of the year. Pool owners in the Valley find themselves constantly filling their pools during the summer due to evaporative losses. If the picture taken is any indication of the number of pools in the Valley, then it can be assumed that their numbers are close to a million or more. If there are 1 million pools in the Valley, each pool has a surface area of 600 square feet and holds 15,000 gallons or more, then there are over 15 billion gallons of water with a combined surface area of 600 million square feet available for evaporation into the Valley’s atmosphere. This does not include water stored in the Los Angeles Reservoir, Pacoima Reservoir, Encino Reservoir, Upper Stone Canyon Reservoir, Green Verdugo Reservoir, the Chatsworth Reservoir, the Hollywood Reservoir, Lake Balboa, Toluca Lake, or any other relatively large body of water in the Valley. The water vapor evaporated from these sources can add to the nighttime urban heat island effect, keeping minimum temperatures warmer than they would be otherwise. This may or may not be true at all elevations below 2000', but it appears to be an influence at and below the 10-15 foot level (it should be noted here that coop and ASOS weather sensors are taking measurements at 5.5 feet above the ground, and that humans live in the lower 6-7 feet of atmosphere above ground level!). This is not to claim that this is a nightly occurrence. Winds and land breezes from surrounding areas can infiltrate the Valley and create enough mixing on some nights to remove excess water vapor.

In addition to man-made bodies of water as sources of water vapor, Valley vegetation may play a noticeable role in warming nighttime temperatures. With suburbanization comes the bucolic love of lawns and green landscapes regardless of the desert environment upon which this imported vegetation is planted. Millions of trees have been planted and millions of lawns have been laid. Almost none of the vegetation in the Valley today could exist without the Department of Water and Power. The Valley was largely devoid of trees up to the early decades of the 20th century (Figs 4.7-4.10). It is a dry Mediterranean climate with only chaparral and desert grasses, but because the Valley has a seemingly unlimited source of fresh water at its disposal, it is able to support lush green lawns and tropical vegetation quite easily.

The combination of moist-climate vegetation in the dry-climate Valley results in unnaturally high transpiration rates between the stomata on leaves and the air immediately above them. It is unnatural because plants could not maintain such high transpiration rates in the Valley if only naturally occurring water supplies were available. In spite of such high vapor pressure gradients between the air and vegetation, vegetation is able to avoid loss of turgon because of constant supplies of water from things like sprinkler systems and garden hoses. It is possible that for areas such as the one shown to the left of Fallbrook Ave. in Figure 4.6, that water vapor pressure is higher below the tree line in heavily suburbanized areas with a relatively high density of lawns, shrubs, and trees.

TEMPERATURE DATA ANOMALIES

There were several anomalies discovered in data calculations that appear not to support the urban heat island theory in the Valley. These anomalies will be addressed together with the station from which the anomalous data was obtained. San Fernando, Burbank, and Sunland each showed temperature anomalies.

San Fernando Temperature Anomalies
Anomalies produced by the San Fernando weather station are decreasing trends in 100°F+ annual maxima, mean temperatures, annual maximum temperatures, and annual minimum temperatures. Though these trends appear anomalous, it must be considered that temperature records from San Fernando cease in 1974. Some of the largest temperature increases occurred in the years after 1974.

Burbank Temperature Anomalies
Anomalies produced by the Burbank weather station are an increase in annual freezing minima and no change in fall minimum temperatures. The latter can simply be due to the fact that Burbank receives the moderating influence of marine air from the Pacific Ocean through the “Narrows”. This could keep fall minimum temperatures from increasing over time. Also, the location of Burbank at an opening in the topographical barrier allows that city to experience more mixing with outside air, which could counter any urban heat island influences.

Sunland Temperature Anomalies
Anomalies produced by the Sunland weather station are decreasing mean summer, winter, and fall temperatures, as well as decreasing spring maximum temperatures. Sunland temperature data only exists from 1950-1965, far too short and terminated too early to be considered justifiably anomalous. Also, Sunland is tucked away between the San Gabriel and Verdugo mountains at an elevation approximately 500 feet higher than other Valley stations.

Conclusions
All available temperature data indicates that the Valley is experiencing a heat island effect. There are gradual increases in temperatures for all seasons and at both monthly temperature extremes. There are increasing trends of annual 100°F+ maxima. There are decreasing trends in annual freezing minima. Diurnal ranges are narrowing in months that experience a strong inversion layer, and increasing in months without such a layer thus suggesting that greenhouse gases are effectively trapped below the inversion created by the Hawaiian High. Statistics point to substantial inputs of greenhouse gases of all types, and it is difficult to deny the fact that such quantities are not at least minimally affecting an urban heat island. In addition to greenhouse gas inputs, the Valley continues to be urbanized as millions of metric tons of additional concrete, asphalt and other high heat capacity materials replace the natural cover of the valley floor.

The network of weather stations is good, but the reinstitution of decommissioned stations would prove extremely useful to the academic, public, and private sectors. There is a plethora of information to be sifted through and more to be collected. Stations should be installed at the old San Fernando site, Sunland site, and some in areas in the central Valley. Though the Valley has abundant rain and temperature data, it is pathetically lacking in wind and atmospheric pollution data. A wealth of information awaits the academic community, but cannot be tackled until the proper network of recording stations is created. A well-established network of recording stations will also help monitor atmospheric variable changes if and when steps are taken to curb the alleged heating trend.

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